Overview

Chronic myelogenous leukemia (CML) is an uncommon type of cancer of the blood cells. The term "chronic" in chronic myelogenous leukemia indicates that this cancer tends to progress more slowly than acute forms of leukemia. The term "myelogenous" (my-uh-LOHJ-uh-nus) in chronic myelogenous leukemia refers to the type of cells affected by this cancer.

Chronic myelogenous leukemia can also be called chronic myeloid leukemia and chronic granulocytic leukemia. Chronic myelogenous leukemia typically affects older adults and rarely occurs in children, though it can occur at any age.

When to see a doctor

Chronic myelogenous leukemia doesn't always reveal itself with obvious signs and symptoms during the early phase. It's possible to live with chronic myelogenous leukemia for months or years without realizing it.

Because people with chronic myelogenous leukemia tend to respond better to treatment when it's started early, make an appointment with your doctor if you have any persistent signs or symptoms that worry you.

Causes

How the Philadelphia chromosome forms

How the Philadelphia chromosome forms

An abnormal chromosome called the Philadelphia chromosome is associated with chronic myelogenous leukemia. Your cells each contain 23 pairs of chromosomes that are made of DNA and hold the instructions for every cell in your body. The Philadelphia chromosome forms when chromosome 9 and chromosome 22 break and exchange portions. This creates an abnormally small chromosome 22 and a new combination of instructions for your cells that can lead to the development of chronic myelogenous leukemia.

Chronic myelogenous leukemia occurs when something goes awry in the genes of your blood cells. It's not clear what initially sets off this process, but doctors have discovered how it progresses into chronic myelogenous leukemia.

First, an abnormal chromosome develops

Human cells normally contain 23 pairs of chromosomes. These chromosomes hold the DNA that contains the instructions (genes) that control the cells in your body. In people with chronic myelogenous leukemia, the chromosomes in the blood cells swap sections with each other. A section of chromosome 9 switches places with a section of chromosome 22, creating an extra-short chromosome 22 and an extra-long chromosome 9.

The extra-short chromosome 22 is called the Philadelphia chromosome, named for the city where it was discovered. The Philadelphia chromosome is present in the blood cells of 90 percent of people with chronic myelogenous leukemia.

Second, the abnormal chromosome creates a new gene

The Philadelphia chromosome creates a new gene. Genes from chromosome 9 combine with genes from chromosome 22 to create a new gene called BCR-ABL. The BCR-ABL gene contains instructions that tell the abnormal blood cell to produce too much of a protein called tyrosine kinase. Tyrosine kinase promotes cancer by allowing certain blood cells to grow out of control.

Third, the new gene allows too many diseased blood cells

Your blood cells originate in the bone marrow, a spongy material inside your bones. When your bone marrow functions normally, it produces immature cells (blood stem cells) in a controlled way. These cells then mature and specialize into the various types of blood cells that circulate in your body — red cells, white cells and platelets.

In chronic myelogenous leukemia, this process doesn't work properly. The tyrosine kinase caused by the BCR-ABL gene causes too many white blood cells. Most or all of these cells contain the abnormal Philadelphia chromosome. The diseased white blood cells don't grow and die like normal cells. The diseased white blood cells build up in huge numbers, crowding out healthy blood cells and damaging the bone marrow.

Risk factors

Factors that increase the risk of chronic myelogenous leukemia:

Older age

Being male

Radiation exposure, such as radiation therapy for certain types of cancer

Family history is not a risk factor

The chromosome mutation that leads to chronic myelogenous leukemia isn't passed from parents to offspring. This mutation is believed to be acquired, meaning it develops after birth.

Complications

Fatigue. If diseased white blood cells crowd out healthy red blood cells, anemia may result. Anemia can make you feel tired and worn down. Treatment for CML also can cause a drop in red blood cells.

Excess bleeding. Blood cells called platelets help control bleeding by plugging small leaks in blood vessels and helping your blood to clot. A shortage of blood platelets (thrombocytopenia) can result in easy bleeding and bruising, including frequent or severe nosebleeds, bleeding from the gums, or tiny red dots caused by bleeding into the skin (petechiae).

Enlarged spleen. Some of the extra blood cells produced when you have CML are stored in the spleen. This can cause the spleen to become swollen or enlarged. The swollen spleen takes up space in your abdomen and makes you feel full even after small meals or causes pain on the left side of your body below your ribs.

Infection. White blood cells help the body fight off infection. Although people with CML have too many white blood cells, these cells are often diseased and don't function properly. As a result, they aren't able to fight infection as well as healthy white cells can. In addition, treatment can cause your white cell count to drop too low (neutropenia), also making you vulnerable to infection.

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